3  B 

4-5 
89 

rc 


UC-MBLF 


George  Davidson 

IftPR-l 911 


INSTRUCTIONS 


FOR    OBSERVING    THE 


TOTAL   ECLIPSE  OF  THE  SOT, 


JANUARY  1,  1889. 


BY   DAVID   P.ITQDT),  PH.D., 

Director  of  Amkerst  College  Observatory. 


AMHEBST,  MASS. 
PUBLISHED   BY   THE  OBSERVATORY. 

1888. 


TOP. 


Obsevv&r. 


Place. 


BOTTOM. 


Tb 


THE 


JANUARY  1,  1889. 


THE  moon's  shadow  sweeps  across  the  Northwestern  United  States  on  the  after- 
noon of  January  1,  1889,  causing  a  total  eclipse  of  the  sun  which  may  be  observed 
in  the  following  regions :  — 

NORTHERN  CENTRAL  CALIFORNIA.  SOUTHEASTERN  MONTANA. 

NORTHERN  NEVADA.  NORTHWESTERN  DAKOTA. 

SOUTHERN  IDAHO.  MANITOBA. 
THE  YELLOWSTONE  PARK. 

Persons  inhabiting  these  localities  can  make  valuable  observations  of  the  eclipse 
by  following  the  directions  indicated  in  this  pamphlet. 

These  observations  are  not  difficult  to  make;  they  mostly  require  no  instruments, 
and  but  little  preparation  beforehand. 

CENTRAL  LINE. 

This  is  the  line  along  which  the  total  eclipse  will  last  the  longest.  It  passes 
through  or  very  near  the  following  points  :  — 

In  California,  Point  Arena,  Manchester,  Boonville,  Ukiah,  Upper  Lake,  Little 
Stony,  Norman,  Nelson,  Brush  Creek,  Nelson  Point. 

In  Nevada,  the  north  end  of  Pyramid  Lake,  Good  Hope,  White  Rock,  Columbia, 
Island  Mountain. 

In  Idaho,  Rock  Creek,  Shoshone  Falls,  Rexburg. 

In  Wyoming,  the  northwest  extremity  of  Yellowstone  Lake. 

In  Montana,  Redlodge,  Dilworth,  Howard,  Forsyth,  Newton,  Ridgelawn. 

In  Dakota,  Fort  Buford,  Little  Muddy. 

In  Manitoba,  Brandon,  Gladstone.  • 


INSTRUCTIONS    FOR    OBSERVING 


PATH  OP  TOTAL  ECLIPSE. 

The  belt,  or  path,  of  total  eclipse  lies  equally  on  both  sides  of  this  central 
line,  and  curves  thus  gradually  toward  the  north.  The  width  of  the  belt  also  grows 
less  toward  the  north  and  east. 

Through  California,  its  average  width  is  about  96  miles.  An  observer,  therefore, 
in  that  State  would  not  expect  to  see  the  sun  entirely  obscured  unless  he  were 
within  48  miles  of  the  central  line,  on  either  side. 

Through  Nevada,  the  average  width  of  the  belt  of  totality  is  about  90  miles  ; 
through  Idaho,  about  82  ;  and  through  Montana,  about  66. 


TIME  AND  LENGTH  OF  TOTAL  ECLIPSE. 

On  the  central  line,  the  time  when  total  eclipse  takes  place,  and  the  duration 
of  the  total  phase,  are  approximately'  as  here  given  :  — 


STATE. 

Time  of  Total  Eclipse. 

Length  of 
Total 
Eclipse. 

California     .     .     . 

1  48  Pacific  Time. 

111.        8. 

1    57 

Nevada   .... 

1  55 

1     48 

Idaho       .... 

3     1  Mountain  Time. 

1     38 

Montana 

36" 

1     25 

Manitoba     .     .     . 

4     8  Central  Time. 

0     12 

GENERAL  APPEARANCE  OF  THE  TOTAL  ECLIPSE. 

Just  before  the  time  indicated  in  the  above  table,  the  sun's  light  will  have 
been  nearly  shut  off  by  the  advancing  moon,  and  it  will  have  become  quite  dark. 
The  only  part  of  the  sun  visible  will  have  the  form  of  a  crescent,  the  ends  of 
which  will  rapidly  approach  each  other  as  the  crescent  becomes  thinner  and 
thinner. 

Immediately  after  the  crescent  has  vanished,  total  eclipse  will  begin,  and  the 
luminous  appendage  of  the  sun,  called  the  corona,  will  become  visible. 

Its  figure  will  be  very  irregular,  and  its  light  very  mild, — in  some  parts  near 
the  edge  of  the  moon  it  may  appear  quite  dazzling,  while  in  other  parts  it 
will  be  extremely  faint,  and  the  streamers  or  filaments  will  appear  to  have  no  defi- 
nite limit. 

This    halo,  or  corona,  can  »be  seen    only  during    a    total    eclipse,    and   it   never 


THE    TOTAL    ECLIPSE   OF   THE   SUN.  5 

looks  twice  alike.  Figs.  1,  2,  and  3  give  some  idea  of  its  appearance  during  past 
eclipses.1 

The  corona  of  the  eclipse  of  1889  is  not  likely  to  resemble  these  in  any  partic- 
ular ;  and  they  are  introduced  here  to  give  a  general  idea  of  the  sort  of  thing  to 
look  for,  and  to  afford  the  observer  an  opportunity  for  practice  beforehand  in  draw- 
ing forms  similar  to  those  he  may  see  during  the  approaching  eclipse. 

In  addition  to  the  mild  white  light  of  the  corona,  there  may  also  be  seen  a  few 
points  of  more  brilliant  light,  but  of  a  reddish  tinge,  appearing  close  to  the  edge  of 
the  moon.  These  are  the  solar  protuberances,  and  they  can  be  advantageously 
observed  only  with  costly  astronomical  instruments.  The  observer  need  not  make 
any  record  of  these. 

USES  OF  OBSERVATIONS  OF  THE  ECLIPSE. 

Much  assistance  will  be  rendered  to  astronomers  who  are  studying  the  corona, 
if  outline  drawings  of  the  whole,  or  any  part  of  it,  are  made,  as  indicated  further 
on.  A  part  of  the  corona  may  be  a  sort  of  solar  atmosphere,  and  is  due  to  the 
presence  of  shining  or  luminous  gas  ,  but  other  parts  seem  to  have  no  necessary 
connection  with  the  sun.  It  is  hoped  that  the  observations  of  this  eclipse  may 
help  to  decide  these  and  other  points  of  interest. 

If  the  observer  is  located  far  from  the  central  line,  the  duration  of  total  eclipse 
is  very  much  shortened.  Thus  there  will  not  be  sufficient  time  for  making  sketches 
of  the  corona. 

If  the  observer  is  located  near  the  northern  edge  of  the  shadow  path  or  near 
its  southern  edge,  he  can  still  make  observations  which  will  be  very  useful  to 
astronomers  ir.  another  way.  All  he  has  to  do  is  to  note  by  the  watch  how  long 
a  time  it  is  from  the  instant  the  last  ray  of  sunlight  disappears,  to  the  time  the 
first  ray  of  sunlight  comes  into  view  after  the  total  eclipse  is  over.  This  will  be 
an  interval  of  time  only  a  few  seconds  long ;  but  with  some  other  details  men- 
tioned subsequently,  it  will  help  astronomers  in  making  very  accurate  predictions 
of  the  position  of  the  moon  in  future  years. 

For  further  reference,  the  different  kinds  of  observation  are  here  classified. 

CLASSES  OF  OBSERVATION  DESIRED. 

CLASS  A.  —  SKETCHES  OF  THE  ENTIRE  CORONA. 

"      B. — SKETCHES  OP  THE  CORONA  NEAR  THE  NORTH  AND  SOUTH  POLES  OF  THE  SUN'S 

DISK. 

"      C.  —  SKETCHES  OF  THE  OUTER  CORONA. 
"      D. — OBSERVATIONS  OF  THE  DURATION  OF  TOTAL  ECLIPSE. 

1  Figs.  1,  2,  3,  4,  and  5  are  taken  from  Professor  Langley's  "  New  Astronomy,"  the  publishers  of 
which,  Messrs.  Ticknor  and  Company  of  Boston,  have  courteously  permitted  their  use  here. 


6  INSTRUCTIONS   FOR   OBSERVING 

Generally  speaking,  it  will  not  be  worth  while  to  attempt  either  A,  B,  or  C,  if 
the  observer  is  more  than  twenty-five  or  thirty  miles  from  the  central  line.  The 
observer  would  do  well  to  attempt  D  in  such  case,  though  observations  of  this  class 
are  of  most  value  when  made  very  near  the  north  and  south  limits  of  the  shadow- 
path. 

This  printed  circular  will  be  received  at  a  few  places  where  several  persons  or 
parties  may  be  found  willing  to  undertake  the  work  indicated.  It  is  desirable  to 
have  many  working  on  the  same  kind  of  observation  at  or  near  the  same  place.  In 
such  case  they  should  be  scattered  over  a  considerable  area,  some  hundreds  or  thou- 
sands of  feet  apart.  In  this  way  a  single  cloud  will  be  less  likely  to  interfere  with 
the  work  of  all.  Each  person  or  party  must  send  off  the  observations  or  drawings 
without  comparing  with  the  work  of  others  at  the  same  place. 

CLASS  A.  —  THE  ENTIRE  CORONA. 

General  drawings  of  the  corona  should  all  be  on  the  same  scale.  A  specimen 
paper  suitable  for  making  such  a  drawing  is  shown  on  the  back  of  the  titlepage. 
A  similar  sheet  may  be  prepared  from  unruled  paper  having  an  unglazed  surface. 
The  straight  lines  are  necessary  to  enable  one  to  draw  the  different  parts  of  the 
corona  in  their  correct  positions. 

It  is  very  desirable  that  the  person  who  will  draw  the  corona  should  have  had 
some  previous  practice  in  sketching  similar  objects.  Otherwise  the  duration  of  total 
eclipse  will  be  found  too  short  to  enable  one  to  draw  the  details  of  the  corona  ac- 
curately. To  facilitate  this  work,  set  up  the  pictures  of  the  corona  in  this  pam- 
phlet (Figs.  1,  2,  and  3),  at  distances  ranging  between  15  and  25  feet,  according 
to  the  quality  of  the  eyes,  and  see  how  much  of  the  detail  of  a  single  picture  can 
be  embodied  in  a  rapid  sketch. 

The  form  of  the  streamers  or  filaments  of  the  corona  is  most  important ;  next,  their 
size  (estimated  in  fractions  of  the  diameter  of  the  dark  disk  in  the  centre,  which 
represents  the  moon) ;  third,  their  brightness  ;  and  lastly,  their  position  around  the 
edge  of  the  disk. 

In  these  practice-drawings  it  would  be  well  to  change  the  position  of  the  picture 
occasionally,  so  that  the  eye  will  become  accustomed  to  the  appearance  of  the  wisps 
of  light,  whether  they  are  directed  up  or  down.  The  time  allowed  for  each  sketch 
should  not  exceed  the  duration  of  totality  in  the  actual  eclipse,  and  this  may  be 
inferred  accurately  enough  from  the  table  on  page  4. 

To  assist  in  drawing  the  coronal  streamers  in  their  accurate  angular  position 
around  the  edge  of  the  moon,  a  plumb-line  will  be  necessary.  Suspend  a  weight 
by  a  strong  white  cord  or  thread  in  such  a  position  that  the  observer,  when  looking 
at  the  corona,  may  see  the  cord  cutting  the  dark  body  of  the  moon  exactly  in  two. 
If  it  is  likely  to  be  windy  during  .the  eclipse,  the  weight  should  hang  freely  in  a 


THE   TOTAL   ECLIPSE   OF   THE   SUN.  7 

basin  of  water ;  or,  after  the  vertical  direction  of  the  cord  has  been  found,  it  may  be 
fastened  at  the  bottom  in  that  position.  It  is  desirable,  but  not  necessary,  that  the 
plumb-line  be  used  in  the  practice-drawings  to  accustom  the  observer  to  its  use 
during  the  eclipse. 

The  light  of  the  corona  may  not  be  bright  enough  to  make  the  drawing  by,  and 
it  is  well  to  provide  artificial  light  which  can  be  used  in  case  it  is  found  necessary. 

Four  or  five  minutes  before  the  eclipse  becomes  total,  close  the  eyes  and  turn 
them  from  the  sun,  so  that  they  will  become  very  sensitive  to  faint  light.  Take  the 
position  previously  arranged  for  making  the  sketch,  with  the  plumb-line  hanging 
between  the  eye  and  the  sun. 

An  attendant  should  watch  the  crescent  of  sunlight,  and  announce  when  the  last 
ray  has  vanished.  The  observer  then  turns  toward  the  sun  and  begins  the  drawing. 
If  no  one  is  present  who  can  do  this,  the  observer  can  himself  look  at  the  diminish- 
ing crescent  through  a  piece  of  smoked  glass,1  taking  great  care  that  no  direct  sun- 
light shall  strike  the  eye.  This  would  be  so  dazzling  as  to  make  it  impossible  to  see 
the  faint  details  of  the  corona  immediately  afterward. 

First,  draw  the  faint  outlines  of  the  corona  as  far  as  they  can  be  seen  from  the 
sun.  It  is  very  important  to  get  their  correct  size  relatively  to  the  moon.  The  lines 
drawn  outward  from  the  black  disk  on  the  prepared  paper  will  be  found  very  useful 
in  marking  the  accurate  positions  of  the  more  prominent  streamers  of  the  corona.  In 
making  this  sketch  it  will  be  best  to  reverse  dark  and  white,  letting  the  white  paper 
represent  the  dark  background  of  the  sky,  while  the  dark  lines  of  the  soft  pencil  will 
represent  the  bright  lines  of  the  corona. 

Then  sketch  the  outlines  of  the  brighter  parts  of  the  corona  all  around  the  edge 
of  the  moon.  If  the  corona  seems  to  dazzle  the  eye,  it  may  be  well  to  view  it 
through  a  piece  of  glass  slightly  smoked.  The  smoked  glass  should  not  be  used  un- 
less the  corona  seems  very  bright,  and  even  then  it  should  be  seen  only  through  the 
thinnest  part  of  the  film. 

After  this  is  done,  if  sunlight  has  not  yet  reappeared,  make  a  rapid  general  com- 
parison of  the  whole  drawing  with  the  corona  itself,  to  correct  any  possible  errors. 
Do  not  try  to  make  a  second  sketch  during  totality,  as  the  time  will  be  too  short. 
The  original  must  not  be  changed  or  corrected  in  any  way  after  sunlight  returns ; 
but  if  the  observer  can  retain  the  appearance  of  the  corona  in  memory,  a  second 

1  This  can  be  made  of  a  small  pane  of  good  window-glass  by  holding  it  over  the  flame  of  a  lamp 
or  candle  until  a  black  film  is  deposited  on  it.  If  possible,  it  should  be  smoked  so  that  the  tint  will 
be  so  dense  at  one  end  that  the  full  light  of  the  sun  seen  through  it  will  not  dazzle  the  eye  ;  while  ai 
the  other  the  film  should  be  so  thin  that  objects  in  an  ordinarily  lighted  room  may  be  seen  distinctly 
through  it.  Smoke  the  glass  as  evenly  as  possible  from  one  end  to  the  other.  Paste  a  narrow  strip 
of  thick  paper  across  each  end  of  the  glass,  on  the  smoked  side,  and  lay  on  it  a  sheet  of  unsmoked 
glass  of  the  same  size.  Then  secure  the  two  sheets  together  by  a  strip  of  paper  pasted  around  the 
edges  of  both  plates. 


8  INSTRUCTIONS    FOR    OBSERVING 

drawing  may  be  made  immediately  on  another  sheet  of  paper,  and  sent  with  the 
original  sketch.  In  this  second  drawing,  black  and  white  need  not  be  reversed,  but 
may  be  drawn  exactly  as  they  appeared  in  the  sky.  • 

The  person  drawing  the  corona  should  not  attempt  to  note  the  exact  time  of  the 
beginning  and  end  of  total  eclipse.  These  data  are  of  no  use  at  points  near  the 
central  line  unless  the  exact  error  of  the  timepiece  is  known.  If  this  has  been 
ascertained,  a  separate  observer  should  record  these  times,  and  should  write  ont  a 
description  of  the  place  where  the  observation  was  made,  exactly  as  indicated  under 
Class  D,  page  14. 

The  name  of  each  observer  should  be  placed  on  the  margin  of  the  drawing,  also 
the  name  of  the  place  where  it  was  made.  No  drawing  should  be  folded  or  creased  ; 
but  all  should  be  forwarded  in  a  pasteboard  roll  or  wrapped  on  a  round  stick  or 
roller.  After  totality  is  over,  and  sunlight  has  begun  to  return,  every  observer  who 
has  been  engaged  in  drawing  will  do  well  to  watch  carefully  for  the  possible  visibility 
of  some  part  of  the  corona.  If  any  parts  can  still  be  seen,  note  their  position,  shape, 
and  size  on  a  separate  sketch,  and  state  how  long  after  totality  they  could  be  seen. 
A  thinly  smoked  glass  will  be  helpful  in  this  observation. 

CLASS  B.  —  CORONAL  DETAILS. 

If  a  field-glass,  spy-glass,  or  telescope  of  any  size  is  available,  the  best  use  it 
can  be  put  to  is  the  observation  of  those  parts  of  the  corona  near  the  poles  of  the 
sun.  These  will  appear  to  the  right  of  the  top  of  the  moon's  edge,  and  to  the  left 
of  the  bottom.  Supposing  the  entire  corona  to  look  somewhat  like  Fig.  3,  the 
poles  will  be  immediately  recognized  as  the  points  which  correspond  to  the  top  and 
bottom  in  this  figure.  In  general,  the  corona  will  probably  be  less  prominently 
marked  near  these  points,  but  the  details  of  the  wisps  of  light  will  be  more  con- 
fused and  complex  ;  and  as  seen  with  the  telescope,  there  may  be  a  slight  resem- 
blance to  Fig.  4,  though  these  exact  forms  are  not  likely  to  reappear  during  the 
coming  eclipse. 

If  the  observer  is  north  of  the  central  line,  he  will  get  better  results  from 
drawing  that  pole  of  the  corona  which  lies  at  the  left  of  the  lowest  point  of  the 
moon's  edge. 

If  the  observer  is  south  of  the  central  line,  he  had  best  sketch  the  corona  at 
the  sun's  northern  pole,  or  that  part  which  will  appear  to  the  right  of  the  upper- 
most part  of  the  moon's  edge. 

The  telescope  or  spy-glass  should  be  firmly  strapped  to  a  round,  upright  post, 
and  pointed  as  nearly  as  possible  in  the  right  direction,  just  before  the  eclipse 
becomes  total.  This  may  be  done  by  protecting  the  eye  with  the  smoked  or  col- 
ored glass ;  and  the  corona  may  appear  so  bright  that  a  very  thin  film  of  smoke 
will  be  found  a  help  in  looking  at  the  parts  close  to  the  sun.  A  lighted  lantern 


THE   TOTAL    ECLIPSE   OP   THE   SUN.  9 

should  be  at  hand  to  illuminate  the  paper  in  case  of  necessity.  Prepare  the  paper 
beforehand,  with  an  arc  of  a  circle  on  it,  similar  to  Fig.  4.  A  plumb-line  will 
be  desirable,  as  described  in  Class  A,  in  order  to  fix  the  angular  position  of  the 
filaments ;  and  the  top  or  bottom  of  the  sun,  as  the  case  may  be,  must  be  marked 
on  the  arc  at  some  time  during  the  progress  of  the  sketch. 

Unless  the  observer  is  used  to  rapid  sketching,  probably  it  will  be  better  to 
attempt  to  draw  the  corona  adjacent  to  a  single  pole  only,  and  thus  save  the  time 
which  would  otherwise  be  lost  in  re-pointing  the  telescope  at  the  other  pole.  It 
is  not  important  which  pole  he  chooses  ;  but  if  there  are  two  telescopes  at  a  given 
place  which  are  to  be  used  in  this  kind  of  observation,  the  observers  should  arrange 
between  themselves  beforehand  to  draw,  one  the  upper  pole,  and  the  other  the 
lower  pole. 

As  much  as  possible  of  the  complexity  of  forms  should  be  rapidly  sketched ; 
and  previous  practice  on  the  curved  and  interlacing  forms  of  Fig.  4  will  be 
serviceable.  The  exact  amount  of  curvature  in  these  forms  is  important ;  also  the 
precise  relations  of  all  the  filaments  should  be  as  accurately  drawn  as  is  found 
practicable.  State  the  name  of  maker  and  size  of  the  telescope,  and  the  mag- 
nifying power,  as  near  as  known. 

Do  not  alter  the  sketch  in  any  respect  after  totality  is  over  ;  but  if  other  details 
than  those  in  the  sketch  are  accurately  remembered,  make  a  second  drawing  at 
once,  and  embody  them  in  that.  A  written  description  of  the  appearance  of  the 
filaments  may  perhaps  contain  additional  information  of  value ;  but  if  such  is 
prepared,  it  should  be  done  immediately  after  the  eclipse  is  over. 

CLASS  C.  —  OUTER  CORONA. 

A  sketch  of  the  outer  corona  and  its  long  streamers  will  be  rather  more  diffi- 
cult to  make  than  the  foregoing,  and  will  require  more  preparation.  Trustworthy 
drawings  will,  however,  be  very  valuable  ;  but  no  one  can  undertake  this  work 
to  advantage  unless  the  eyes  are  very  sensitive  to  faint  light. 

Fig.  5  shows  the  appearance  of  these  streamers  during  the  eclipse  of  1878. 
It  is  not  absolutely  certain  that  they  will  be  visible  during  the  eclipse  of  1889; 
but  they  should  be  carefully  looked  for,  taking  the  precautions  indicated  be- 
low. It  will  be  well  to  practise  the  sketching  of  Fig.  5  in  outline  beforehand, 
so  that  any  similar  forms  which  will  likely  appear  during  the  eclipse  may  be  rap- 
idly and  accurately  put  on  paper.  For  this  purpose  place  it  8  or  10  feet  from 
the  eye. 

The  inner  corona  is  so  bright  that  if  the  eye  looks  at  the  eclipse  directly,  the 
faint  light  of  the  long  streamers  cannot  be  seen.  In  order  to  see  them,  therefore, 
it  will  be  necessary  to  set  up  a  disk  in  line  with  the  eye  and  the  sun,  so  as  to 
screen  the  eye  from  the  brighter  light  of  the  inner  corona.  Any  round  disk,  cut 


10 


INSTRUCTIONS   FOR   OBSERVING 


out  of  wood,  pasteboard,  or  sheet  iron,  will  answer  the  purpose  ;  and  it  will  be 
well  to  paint  it  a  dead  black,  though  this  is  not  necessary. 

Attach  a  slender  rod  or  pole  to  the  disk,  and  then  fasten  the  whole  securely 
to  the  gable  of  a  house,  the  top  of  a  telegraph  pole,  or  some  other  object,  so  that 
it  may  be  exactly  in  line  with  the  sun  at  the  time  of  totality.  The  rod  or  pole 
should  be  at  least  3*  or  4  feet  long,  and  should  be  fastened  up  plumb.  The 
view  all  around  the  disk  should  be  unobstructed,  except  by  the  rod  which  supports 
it ;  especially  on  the  east  and  west  sides  of  the  disk,  there  should  be  no  objects 
within  nearer  range  than  12  or  15  feet. 

The  size  of  the  disk  will  vary  with  its  distance  from  the  eye  of  the  observer ; 
and  he  must  first  select  the  most  available  place  for  setting  up  the  disk  and  making 
the  observation,  and  then  cut  the  disk  of  the  right  size  to  correspond  with  the 
distance  from  the  eye  at  which  it  will  be  set  up.  This  table  will  show  the  proper 
size  for  the  disk  to  suit  any  distance  from  20  feet  to  90  feet. 


Distance  of  Disk 
from  the  Bye. 

Corresponding 
Diameter  of  Disk. 

Distance  of  Disk 
from  the  Eye. 

Corresponding 
Diameter  of  Disk. 

20  feet. 
25    » 
30    " 
35    " 

4-f  inches. 
6f      « 

6|      « 
8 

60  feet. 
65    « 
70    " 
75    « 

13|  inches. 
14f      « 
15|      «« 
17 

40    " 

9i     " 

80    " 

18|      " 

45    " 

104-      " 

85    " 

194-      " 

50    " 
55    « 

i"i  •• 

90    " 

20f     « 

Any  distance  within  this  range  will  be  suitable,  but  an  average  distance  of  50  to 
70  feet  will  be  somewhat  preferable  to  either  extreme. 

Having  set  up  the  disk,  the  observer  must  next  arrange  for  the  exact  position 
of  the  eye  during  the  eclipse,  as  nearly  as  possible.  This  may  be  done  in  the 
following  way.  A  few  days  before  the  eclipse,  note  where  the  shadow  of  the 
disk  falls,  at  the  hour  when  the  eclipse  is  to  be  total  on  eclipse  day.  This  time 
can  be  obtained  nearly  enough  from  the  table  on  page  4. 

The  point  where  the  centre  of  the  shadow  falls  will  be  very  near  the  position 
where  the  eye  should  be,  when  looking  at  the  eclipse ;  its  distance  from  the 
disk,  of  course,  being  that  corresponding  to  the  size  of  the  disk.  Cut  out  a  light 
disk  of  diameter  one  inch  larger  than  the  disk  attached  to  the  pole,  and  mark 
its  centre.  Hold  it  so  that  the  shadow  of  the  first  disk  shall  fall  centrally  upon 
it,  at  the  time  when  the  eclipse  is  to  be  total.  Then  make  a  permanent  mark 
where  the  centre  of  the  light  disk  is,  by  means  of  an  index  or  pointer.  In  this 


THE   TOTAL   ECLIPSE  OP   THE   SUN.  11 

way  the  observer   will  know  very  nearly  where  to  place   the  eye  at   the  proper 
time,  on  eclipse  da}%  and  not  lose  any  time  in  the  operation. 

The  index  should  be  fastened  at  its  upper  end,  and  point  downward,  the  lower 
end  of  it  coinciding  as  nearly  as  possible  with  the  centre  of  the  shadow  of  the  dark 
disk.  Each  day  before  the  eclipse,  the  position  of  the  pointer  should  be  verified ; 
and  it, will  be  found  that  it  must  be  moved  down,  and  toward  the  west,  a  fraction 
of  an  inch  each  day.  It  is  especially  important  that  this  test  should  be  made  on 
the  two  days  immediately  before  the  eclipse. 

Prepare  a  sheet  of  paper  for  the  drawing,  putting  a  dark  circle  in  the  centre, 
similar  to  the  figure  at  the  front,  but  only  one-half  an  inch  in  diameter.  A  lighted 
lantern  should  be  provided,  to  illuminate  the  paper,  as  it  may  be  necessary  in  making, 
the  sketch ;  but  a  shield  must  be  placed  over  it,  to  keep  its  direct  light  from 
reaching  the  eyes  of  the  observer. 

Ten  or  fifteen  minutes  before  the  eclipse  will  become  total,  the  observer  must 
go  into  a  very  dark  room,  in  order  that  the  eyes  may  become  as  sensitive  as 
possible.  This  room  should  be  within  a  few  feet  of  the  point  of  observation.  An 
assistant  then  announces  when  the  last  ray  of  sunlight  has  gone  and  the  corona 
has  made  its  appearance.  Then,  with  eyes  closed,  the  observer  takes  the  position 
at  the  pointer.  Not  until  sure  that  the  eyes  are  in  the  correct  position,  close  to 
the  lower  end  of  the  pointer,  should  the  eyes  be  opened. 

In  a  few  seconds  the  long,  indefinite  streamers  of  the  corona  will  likely  be- 
come visible,  extending  outward  faintly  a  long  distance  to  the  left  and  somewhat 
upward ;  also  to  the  right  and  somewhat  downward.  They  may  look  a  little 
like  the  long  streamers  in  Fig.  5 ;  but  that  is  not  certain. 

All  of  the  brighter  part  of  the  inner  corona  will  be  hidden  behind  the  disk, 
when  the  eyes  are  kept  in  position  at  the  end  of  the  pointer  ;  and  while  looking 
for  the  faint  streamers,  the  observer  should  be  particularly  careful  not  to  move  the 
head  up  or  down,  or  to  the  right  and  left,  as  this  brighter  light  would  then  strike 
the  eye,  and  spoil  the  chances  of  seeing  the  faint,  outlying  streamers. 

If  the  eye  catches  a  glimpse  of  these  objects,  first  notice  whether  the  bands  are 
of  the  same  width  on  both  sides  of  the  disk,  whether  they  are  as  wide  in  any  part 
as  the  disk  is,  and  whether  they  extend  to  the  same  distance  from  the  disk  on  both 
sides. 

Be  especially  careful  to  observe  how  far  out  the  streamers  extend,  estimating 
their  length  in  diameters  of  the  disk.  Note  also  their  angular  direction,  relatively 
to  the  vertical  pole  which  supports  the  disk.  Sketch  all  these  points  as  rapidly  as 
possible.  Also  observe  whether  the  streamers  on  both  sides  form  parallel  bands 
of  light,  or  whether  they  are  slightly  divergent,  as  in  the  lower  part  of  Fig.  5  ; 
also  whether  they  are  equally  bright  throughout,  or  whether  they  are  quite  bright 
in  some  parts,  and  very  faint  in  others. 

All  details  of  their  structure  should  be  as  carefully  recorded  as  possible,  in  the 


12  INSTRUCTIONS    FOR    OBSERVING 

rapid  sketch;  and  the  observer  should  make  out,  if  practicable,  whether  the  ends  of 
the  streamers  are  alike  —  or  different,  somewhat  resembling  Fig.  5. 

The  sketch  actually  made  during  the  eclipse  should  not  under  any  circum- 
stances be  altered  afterward  ;  but  if  the  observer  saw  additional  features  which 
he  can  carry  in  memory,  these  may  be  embodied  in  a  second  drawing  which 
should  be  finished  immediately.  Descriptions  of  certain  features  by  letter  will  be 
valuable,  if  the  observer  could  not  succeed  in  drawing  them  satisfactorily*  The 
sketches  should  be  sent  off  without  any  comparison  with  the  similar  work  of 
others.  State  the  size  of  the  dark  disk,  and  its  distance  from  the  eye. 

CLASS  D.  —  SIMPLE  DURATION  OF  TOTALITY, 

To  make  this  observation  to  good  advantage,  the  observer  should  be  located 
within  a  few  miles  of  the  north  or  south  edge  of  the  shadow-path.  The  instruc- 
tions here  following  are  essentially  the  same  as  those  prepared  by  Professor  New- 
comb  for  the  Eclipse  of  1878. 

INSTRUMENTS. 

The  only  indispensable  instrument  is  a  good  watch,  provided  with  a  seconds- 
hand,  and  having  a  white  face.  The  minute-hand  should  be  carefully  set  so  as 
to  be  on  an  exact  minute  when  the  seconds-hand  is  at  60s-  This  being  done,  it 
is  no  matter  how  far  wrong  the  watch  may  be. 

A  good  auxiliary  will  be  a  common  spy-glass  lashed  to  a  round  post,  so  as  to 
be  steady  enough  to 'give  an  easy  view  of  the  sun.  To  lessen  the  brilliancy  of 
the  sun,  cover  the  object-glass  with  a  cap  having  a  round  hole  three  fourths  of 
an  inch  in  diameter  cut  in  its  centre.  The  spy-glass-  will  be  worse  than  useless 
unless  one  is  accustomed  to  its  use,  and  has  it  fastened  so  as  to  be  steady.  An 
opera-glass  held  in  the  hand  might  also  serve  a  good  purpose.  A  smoked  glass 
should  also  be  prepared,  but  a  part  of  the  glass  should  be  only  very  lightly 
smoked.  See  foot-note,  page  7. 

ARRANGEMENT  FOR  OBSERVATION. 

Each  observation  should  be  made  by  a  party  of  three  persons.  Only  one  in- 
strument of  each  kind,  watch,  glass,  etc.,  is  needed  by  a  party.  A  station  should 
be  selected  where  they  will  be  free  from  all  interruption,  either  in  the  open  air 
or  at  an  open  window  facing  west.  One,  at  least,  of  the  party  must  have  a  pen- 
cil and  note-book  in  hand  to  record  the  time. 

THE  OBSERVATION. 

When  the  visible  part  of  the  sun  is  reduced  to  the  narrowest  crescent,  the 
holder  of  the  watch,  keeping  his  eye  on  its  face,  will  begin  to  count  the  seconds 


THE   TOTAL   ECLIPSE   OP   THE   SUN.  13 

aloud.  The  observers  of  each  party  should  practise  beforehand  the  counting,  call- 
ing, and  recording.  The  holder  of  the  smoked  glass,  with  or  without  the  spy- 
glass, will  watch  for  the  last  ray  of  true  sunlight,  being  careful  to  look  through 
the  brightest  part  of  the  glass  which  the  eye  will  bear  without  inconvenience. 
The  third  observer,  if  there  be  one,  will  look  for  the  disappearance  of  sunlight 
with  the  naked  eye,  and  stand  ready  with  pencil  and  paper  to  record  the  time. 
When  the  last  ray  of  the  sun  has  disappeared,  the  observer  with  the  glass  will 
call  time;  and  the  exact  second  at  which  the  call  was  given  must  be  immediately 
written  down.  The  minute,  also,  must  be  carefully  noted  and  recorded.  The 
observers  will  then  await  the  return  of  sunlight,  the  count  of  seconds  being  kept 
up,  if  the  face  of  the  watch  can  be  seen,  which  it  probably  can,  when  held  so  that 
the  light  of  the  corona  shall  fall  upon  it. 

The  first  flash  of  true  sunlight  will  seem  to  burst  out  suddenly,  and  the  min- 
ute and  second  of  its  appearance  must  be  recorded  with  the  same  care  as  the 
time  of  disappearance.  The  difference  of  the  two  times  gives  the  duration  of 
totality. 

If  the  observer  has  a  stop-watch,  he  can  readily  record  the  contacts  without 
any  assistance.  Set  the  stop  watch  at  o"1  o%  and  at  the  instant  of  the  beginning 
of  total  obscuration,  start  it.  When  totality  ends,  stop  the  watch,  and  its  reading 
will  then  furnish  the  quantity  desired. 

SPECIAL  PRECAUTIONS. 

In  judging  the  beginning  of  totality,  there  is  danger  of  error  from  two  sources. 
The  first  is  that  the  sun's  crescent  may  become  so  narrow  as  to  become  invisible 
through  the  smoked  glass,  if  it  be  too  dark,  several  seconds  before  it  is  really  all 
covered  ;  and  thus  the  observer  may  call  "  time  "  too  soon.  Such  a  mistake  may 
be  detected  and  corrected  by  the  third  observer,  looking  on  with  the  naked  eye, 
if  the  following  circumstance  be  attended  to:  — 

The  beginning  of  total  eclipse  is  marked  by  a  very  rapid  increase  in  the  darkness 
caused  by  the  advent  of  the  moon's  shadow.  If,  then,  the  darkness  increases  more 
rapidly  after  time  is  called  than  it  did  before,  time  was  called  too  soon,  and  must  be 
repeated.  The  other  danger  is  of  the  opposite  kind,  and  should  be  equally  avoided. 
It  is  that  the  light  of  the  brilliant  rose-colored  protuberances  which  surround  the 
dark  body  of  the  moon  during  the  total  eclipse  may  be  mistaken  for  sunlight,  and 
thus  the  critical  moment  be  suffered  to  pass.  In  this  case  each  observer  must  de- 
termine separately  as  to  the  exact  second  at  which  it  ceased  to  grow  darker;  and  if 
they  agree  within  one  or  two  seconds,  the  time  judged  may  be  supposed  correct,  and 
each  one's  estimate  may  be  written  down  separately.  The  observer  with  the  smoked 
glass  will  be  more  liable  to  the  former  of  these  mistakes  ;  the  naked-eye  observer, 
to  the  latter. 


14  INSTRUCTIONS    FOR    OBSERVING    THE   TOTAL    ECLIPSE   OP   THE   SUN. 

The  return  of  sunlight  will  also  be  preceded  by  a  reddish  glow  on  the  border  ot 
the  dark  moon,  which  must  not  be  mistaken  for  the  sun.  Indeed,  if  the  observer  be 
near  the  edge  of  the  shadow,  it  is  probable  that  this  red  glow,  which  comes  from  the 
hydrogen  atmosphere  of  the  sun,  may  be  visible  during  the  whole  time  of  totality. 

All  the  recorded  times,  with  an  estimate  of  the  uncertainties  to  which  the  ob- 
servers think  they  were  liable,  and  a  statement  of  the  place  where  made,  should  be 
immediately  certified  by  the  signatures  of  all  three  observers. 

In  order  to  facilitate  the  subsequent  determination  of  the  longitude  and  latitude 
of  the  place  of  observation,  state  the  distance  and  direction  of  this  point  from  the 
nearest  telegraph-office,  post-office,  or  other  recognized  landmark. 

It  is  particularly  requested  that  each  party  shall  send  off  its  report  before  com- 
paring notes  with  any  other  party  ;  also  that  the  original  pencil  record,  however 
imperfect,  accompany  the  report. 

All  drawings  or  observations  of  the  eclipse  made  in  response  to  these  instructions 
should  be  promptly  mailed  to 

PROF.  DAVID  P.  TODD, 
Amherst  College  Observatory,  Amherst,  Mass. 


To  PHOTOGRAPHERS. 

Fasten  an  ordinary  newspaper  smoothly  on  a  frame  or  board,  and  set  it  up 
about  4  feet  from  the  ground,  and  perpendicular  to  a  line  drawn  toward  the  sun 
at  the  time  of  total  eclipse.  Leave  that  side  of  the  paper  out  which  shows  the 
greatest  variety  of  type.  Set  up  an  ordinary  camera  on  the  ground  directly  in  front 
of  the  paper,  and  so  that  its  lens  is  15  feet  from  the  frame.  Bring  the  paper 
into  the  centre  of  the  field,  and  focus  upon  it  carefully.-  Use  the  most  sensitive  dry- 
plate  available.  Make  sure  that  the  lenses  are  thoroughly  cleaned,  and  use  no 
diaphragms. 

Wait  about  ten  seconds  after  the  corona  has  become  visible,  and  then  begin  the 
exposure.  Time  this  to  sixty  seconds  as  accurately  as  possible.  Should  the  photo- 
grapher be  more  than  twenty-five  miles  distant  from  the  central  line,  begin  the  ex- 
posure immediately  after  the  corona  becomes  visible  ;  and  if  totality  does  not  last 
sixty  seconds,  put  on  the  cap  just  before  sunlight  reappears,  and  record  the  length  of 
the  exposure.  , 

Make  a  memorandum  also  of  the  state  of  the  sky,  the  name  of  the  place,  the 
camera  used,  the  name  of  the  maker,  size  and  quality  of  lens,  and  the  kind  of  dry- 
plate,  and  its  number  or  name.  Send  the  memoranda,  with  the  newspaper,  the  ex- 
posed plate  (undeveloped),  and  a  duplicate  unexposed  dry-plate,  to  the  address  given 
above. 


Fie.  1.  —  OCTER  CORONA  OF  1869. 


FIG.  2.  —  CORONA  OF  1870. 


FIG.  o.  —  CORONA  OF  1871. 


FIG.  4.  —  DKTAILS  OF  PART  OF  FIG.  :>. 


FIG.  5.  —  OUTER  CORONA  OF  1878. 


